The goal of this Phase I SBIR proposal is to demonstrate utility to all major pathogenic bacterial strains of SeLux?s rapid, low-cost, phenotypic antibiotic susceptibility test (AST) system (fast-AST or FAST). Utilizing existing optical detectors and standard dried antibiotic microplates, and avoiding pitfalls of metabolic probes, FAST will potentially transform therapy of infections by significantly accelerating AST, thereby facilitating treatment with the optimal antibiotic. Aim 1 will apply FAST to hundreds of samples of pathogenic bacterial strains, while developing and optimizing a predictive algorithm for clinical utility. Aim 2 will extend the FAST platform to slow-growing strains and species as well. SeLux has demonstrated FAST to exceed FDA 510(k) requirements for minimum inhibitory concentration determinations for 25+ strains of Staphylococcus aureus and Escherichia coli with full antibiotic panels. Completion of the proposed aims will expand FAST to all major clinically-relevant, non-fastidious bacterial pathogens. SeLux?s interdisciplinary team has expertise in nanosensing, microbiology, and algorithm design and is buttressed by distinguished experts in Clinical Microbiology, Infectious Disease, and Machine Learning.